Where pigments and dyes are used in various products as a colorant, it has heretofore been known to be necessary to carry out a pretreatment of the dyes and pigments with an atomizer, roll mill, or sand mill for the purpose of grinding the aggregated pigments and dyes to thereby stabilize their coloration. In such a conventional method, however, selection of the pretreatment conditions is difficult, since the respective pigments and dyes have different cohesive forces. In addition, since some pigments and dyes do not have sufficient dispersion stability, reaggregation of the pulverized particles occurs. Consequently, conventional methods have the drawback of not yielding good coloration.
As a technique for overcoming this drawback of the prior art, Japanese Patent Application Laid-Open No. 62-91565, (U.S. 4,806,128) for example, has proposed a method of obtaining a pigment material with good color by adding a finely powdered flaky substrate to an aqueous solution of a dye, followed by precipitating and depositing dye particles on the surface of the substrate.
Japanese Patent Application Laid-Open No. 63-243168 (U.S. 4,755,229) has proposed formation of a colored mica pigment by precipitating pigment particles on the surfaces of substrates in an aqueous system so as to cover the substrates with the precipitated pigment.
However, since the improved methods in the prior art are so-called wet methods in which treatment is effected in a liquid medium, they require filtration and drying steps so that the cost for manufacturing the product is high. In addition, since dispersion of fine particles of pigments and dyes is often poor, good coloration could not be attained. Thus, the known methods still have drawbacks. Moreover, the pigment or dye particles which have not adhered to the surfaces of the substrates, loosely adhering pigment or dye particles, and excess particles from the pretreatment step would be separated or washed out during the subsequent filtering step or washing step. In this case, sufficient coloration would not be attained in proportion to the amount of the dye or pigment used.